1. Field
The presently disclosed subject matter relates to vehicle headlights using a semiconductor light source, and more particularly to vehicle headlights including a radiation structure having a high radiation performance and positional accuracy for the semiconductor light source, which can prevent a positional misalignment of the semiconductor light source caused by variability due to an inclusion disposed in a thermal conductive viscous material.
2. Description of the Related Art
Various vehicle headlights incorporating a semiconductor light source have been developed in recent years because semiconductor light sources are battery friendly (lower power requirements), have long life, and are generally more eco-friendly, etc. For example, a conventional LED light source and a vehicle lamp using the LED light source are disclosed in Patent Document No. 1 (U.S. Pat. No. 7,520,647). The conventional LED light source disclosed in Patent Document No. 1 can be used as a light source for a reflector type vehicle headlight.
When the conventional LED light source described above is used for a vehicle headlight, the headlight may form a light distribution pattern by reflecting light emitted from the LED light source of the reflector. When a light distribution pattern for a low beam is formed by the LED light source and the reflector, the vehicle headlight may form a light distribution pattern for a low beam including a horizontal cut-off line by shielding an upward light by using a shade besides the reflector.
A light source for a vehicle headlight of a projector type that does not include a reflector and the shade is disclosed in co-pending commonly assigned Patent Document No. 2 Ser. No. 13/070,707. This conventional semiconductor light-emitting device may form a light distribution pattern for a low beam including a horizontal cut-off line via a projector lens without a reflector and a shade.
High power semiconductor light-emitting devices have recently been utilized as the light source for vehicle headlights in accordance with a trend toward miniaturization of the vehicle headlight, creating an appearance of a semiconductor device having a high brightness, the need for an eco-friendly vehicle and improved driving safely, etc. However, because high power semiconductor devices may generate a large amount of heat, various radiating/heat dissipation methods for high power semiconductor devices have been devised.
For example, a thermal conductive grease and a semiconductor device using the thermal conductive grease are disclosed in Patent Document No. 3 (Japanese Patent Application Laid Open No. 2000-63873). FIG. 11 is a cross-section view depicting the conventional semiconductor device including a radiation structure disclosed in Patent Document No. 3. The semiconductor device includes: a printed circuit board 203; a semiconductor chip 202 generating a large amount of heat that is mounted on the printed circuit board 203; a heat sink 204 located on the semiconductor chip 202; a thermal conductive grease 201 disposed between the semiconductor chip 202 and the heat sink 204; and cramping plates 205 attaching the heat sink 204 to the printed circuit board 203.
Therefore, because a large amount of heat generated from the semiconductor chip 202 may radiate from the heat sink 204 via the thermal conductive grease 201, the semiconductor device may operate normally even under high temperatures. In this case, the thermal conductive grease 201 includes a powder of aluminum to enhance the thermal conductivity thereof, and a mean particle size of the aluminum powder may be between 0.5 micrometers and 50 micrometers.
FIG. 10a is a cross-section view depicting a conventional vehicle headlight including a radiation structure. The conventional headlight 200 of FIG. 10a includes: a semiconductor light source 210; a thermal conductive grease 240 disposed underneath the semiconductor light source 210; a heat sink 230 located underneath the semiconductor light source 210 via the thermal conductive grease 240; and a reflector 220 located on the heat sink 230 so that light rays emitted from the semiconductor light source 210 are reflected in a light-emitting direction of the headlight 200.
The conventional headlight 200 can form a prescribed light distribution pattern with the light rays emitted from the semiconductor light source 210, which can conform to a light distribution standard for a headlight. Additionally, the headlight 200 can efficiently radiate heat developed from the semiconductor light source 210 from the heat sink 230 via the thermal conductive grease 240. However, when mass-producing the vehicle headlight 200, some products that form light distribution patterns that may not conform to the light distribution standards for a headlights are produced.
FIGS. 10b and 10c are explanatory cross-section views depicting conventional headlights when causing an upward light distribution and when causing a downward light distribution, respectively. Light Ray1 shown in FIG. 10a can fundamentally be emitted in a horizontal direction with respect to a road. However, the light Ray1 of FIG. 10a may change to an upward light Ray1-U in FIG. 10b. Accordingly, because the upward light Ray1-U may give a glaring type light to an oncoming vehicle, a light distribution pattern formed by a headlight shown in FIG. 10b may not conform to the light distribution pattern for a headlight.
In contrast, the light ray1 shown in FIG. 10a changes to a downward light Ray1-D in FIG. 10c. Therefore, because the downward light Ray1-D forms a downward light distribution, forward visibility may be reduced in comparison with the normal headlight 200 shown in FIG. 10a. In addition to the above-described cases, light distribution patterns that slant rightward or leftward may also be formed. When a reflective surface of the reflector 220 is configured with a plurality of free surfaces that need a high positional accuracy, the vehicle headlight 200 is subject to emission of the abnormal lights.
This is due to a variability in the particle size of an inclusion in the thermal conductive grease 240, and thereby the semiconductor light source 210 is likely to slant. Additionally, it is difficult to confirm whether the thermal conductive grease 240 spreads wholly between the heat sink 230 and the semiconductor light source 210 or not. If products having a thermal conductive grease 240 that does not spread between the heat sink 230 and the semiconductor light source 210 are used for a long time under a severe environment of a high temperature, some of the products may break down.
The above-referenced Patent Documents are listed below, and are hereby incorporated with their English abstracts in their entireties.    1. Patent Document No. 1: U.S. Pat. No. 7,520,647    2. Patent Document No. 2: Commonly owned patent application Ser. No. 13/070,707.    3. Patent Document No. 2: Japanese Patent Application Laid Open No. JP2000-63873
The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, embodiments of the disclosed subject matter can include vehicle headlights using a semiconductor light source that include a radiation structure having high radiation performance and positional accuracy for the semiconductor light source. The disclosed subject matter can also include a vehicle headlight that is configured such that it is relatively easy to confirm an applying state of a thermal conductive material through visual examination, especially whether the thermal conductive material is normally disposed between the heat sink and the semiconductor light source, and thus the amount of defective products such as described above can be reduced.